Excess current protective component

Abstract: An electronic component constructed by elastically interposing an electronic component element 13 between a pair of spring terminals 14 and 15, in which contact portions 17 and 18, which are respectively brought into contact with electrodes 13b and 13c of the electronic component element 13, of the spring terminals 14 and 15 are not opposed to each other on both major surfaces of the electronic component element 13, and at least one of grooves 16a to 16c for guiding the direction in which the electronic component element 13 is divided is formed on both the major surfaces of the electronic component element 13.

Description: The present invention relates generally to an electronic component having a structure formed by elastically interposing an electronic component element between a pair of spring terminals, and more particularly, to an electronic component having a structure capable of preventing accidents caused by the destruction of an electronic component element in the case of an abnormality. Description of the Prior Art Fig. 5 is a cross sectional view showing a positive temperature coefficient thermistor (hereinafter referred to as a PTC) device as one example of known electronic components. In a PTC device 1, a PTC element 3 is contained in a case 2 made of synthetic resin. The case 2 comprises a case body 2a having an opening formed in its upper part and a cover member 2b for closing the opening. The PTC element 3 has a structure in which electrodes 3b and 3c are formed on both major surfaces of a plate-shaped thermistor body 3a. Elastic portions 4a and 5a of spring terminals 4 and 5 are brought into contact with the electrodes 3b and 3c, so that the spring terminals 4 and 5 are electrically connected to the electrodes 3b and 3c, respectively. The spring terminals 4 and 5 are not only electrically connected to the electrodes 3b and 3c by the elastic portions 4a and 5a but also hold the PTC element 3 elastically interposed therebetween to put the PTC element 3 in a predetermined position in the case 2. In this structure, portions, which are respectively brought into contact with the electrodes 3b and 3c, of the elastic portions 4a and 5a, that is, contact portions 4b and 5b are opposed to each other while being separated by the PTC element 3. An example of one of these prior art's components can be formed in the PATENT ABSTRACTS of JAPAN, vol. 16, no. 294 (E-1225) 29 June 1992 & JP-A-04 078 103 (MURATA MFG CO LTD) 12 March 1992. In the PTC device 1, however, an abnormal voltage exceeding a rated voltage may, in some cases, be applied to the PTC element 3 depending on any circumstances. Also, the PTC element 3 may, in some cases, be degraded due to, for example, the change in the environment. As a result, the PTC element 3 is destroyed while it is being used, so that PTC element pieces 3A and 3B formed by the destruction may, in some cases, be scattered in the case 2. In the conventional PTC device 1, however, the PTC element piece 3A remains elastically interposed between the spring terminals 4 and 5 even if the PTC element 3 is destroyed, as indicated by the PTC element piece 3A shown in Fig. 6. That is, an energized state may be continued in the PTC element piece 3A after the destruction. SUMMARY OF THE INVENTION An object of the present invention is to provide, in an electronic component having a structure formed by elastically interposing an electronic component element between spring terminals, the electronic component capable of reliably preventing element pieces from being energized even if the electronic component element is destroyed in the case of an abnormality. The present invention is directed to an electronic component comprising an electronic component element having electrodes formed on both its major surfaces, and a pair of spring terminals electrically connected to the electrodes of the electronic component element and holding the electronic component element elastically interposed therebetween, which is characterized by having the following structure. Specifically, the electronic component according to the present invention is characterized by the characterizing features of claim 1. In the present invention, the above described pair of spring terminals are respectively brought into contact with the electrodes of the electronic component element so that the portions, which are brought into contact with the electrodes, of the spring terminals having the electronic component element interposed therebetween are not opposed to each other. When the electronic component element is destroyed at the time of an abnormality, therefore, pressures applied from the spring terminals to electronic component element pieces formed by the destruction are exerted on different positions on both the major surfaces of the electronic component element, thereby to make it difficult to elastically interpose the electronic component element pieces between the pair of spring terminals. As a result, the electronic component element pieces are reliably prevented from being energized. Furthermore, in the case of the destruction, at least one groove for guiding the direction, in which the electronic component element is cracked, is formed on at least one of both the major surfaces of the electronic component element, so that the electronic component element is reliably destroyed along the groove. Consequently, the electronic component element is reliably destroyed at the time of an abnormality, to be divided into a plurality of electronic component element pieces. Accordingly, it is possible to reliably prevent the electronic component element pieces from being energized, combined with the function of the pair of spring terminals. When the electronic component element is destroyed due to, for example, the application of an abnormal voltage or the change in the environment, therefore, the electrically connected state between the plurality of electronic component element pieces formed by the destruction and the spring terminals is reliably released, thereby to make it possible to reliably prevent the electronic component element pieces from being energized after the electronic component element is destroyed. In accordance with a particular aspect of the present invention, only one of the pair of spring terminals is brought into contact with the electrode in at least one of a plurality of regions separated by the at least one groove on at least one of the major surfaces of the electronic component element. In this case, in a region where only one of the pair of spring terminals is brought into contact with the electrode, a force from only one spring terminal is applied to the electronic component element in the region if the electronic component element is destroyed along the groove, thereby to make it possible to disperse the electronic component element pieces more effectively. More preferably, in each of the plurality of regions separated by the at least one groove, only one of the pair of spring terminals is brought into contact with the electrode, thereby to disperse the electronic component element pieces obtained by dividing the electronic component element along the groove more effectively. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B are respectively a schematic front view and a side view for explaining the relationship between elastic portions of spring terminals and a PTC element in a first embodiment of the present invention; Fig. 2 is a cross sectional view showing a PTC device according to the first embodiment; Figs. 3A and 3B are respectively partially cutaway enlarged sectional views for explaining the relationship between a groove and an electrode; Figs. 4A and 4B are respectively a schematic front view and a side view for explaining the relationship between spring terminals and a PTC element in a PTC device according to a second embodiment; Fig. 5 is a cross sectional view showing a conventional PTC device; and Fig. 6 is a cross sectional view for explaining the problem of the conventional PTC device. DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-restrictive embodiment of the present invention will be described to clarify the present invention. Fig. 2 is a cross sectional view showing a PTC device according to one embodiment of the present invention. A PTC device 11 comprises a case 12 made of synthetic resin which is constituted by a case body 12a having an opening in its upper part and a cover member 12b for closing the opening. A PTC element 13 is contained in the case 12. The PTC element 13 has a structure in which electrodes 13b and 13c are formed on the entire major surfaces of a disk-shaped PTC body 13a. The PTC element 13 is elastically interposed between spring terminals 14 and 15 in the case 12. The spring terminals 14 and 15 respectively have elastic portions 14a and 15a which are brought into elastic contact with the electrodes 13b and 13c in the case 12. The relationship between the elastic portions 14a and 15a and the PTC element 13 will be described with reference to Figs. 1A and 1B. Fig. 1A is a diagram as viewed from the elastic portion 14a of the one spring terminal 14, where the position of the elastic portion 15a of the other spring terminal 15 formed on the major surface on the opposite side of the PTC element 13 is illustrated by oblique hatching. As apparent from Figs. 1A and 1B, the elastic portions 14a and 15a of the spring terminals 14 and 15 respectively have branched portions extending in a radial manner in three directions from the center of the PTC element 13, and contact portions 17 and 18 which are brought into direct contact with the electrodes 13b and 13c are formed in the vicinities of ends of the branched portions. In the present embodiment, the branched portions are not opposed to each other on both the major surfaces of the PTC element 13, so that the contact portions 17 and 18 are not opposed to each other on both the major surfaces of the PTC element 13. Although in Fig. 1A, the elastic portions 14a and 15a are respectively in a shape having branched portions extending in a radial manner in three directions from the center of the PTC element, the elastic portions 14a and 15a may be constructed in another shape so long as the contact portions 17 and 18 of the elastic portions 14a and 15a are in positions where they are not opposed to each other while being separated by the PTC element 13 and the PTC element 13 can be elastically interposed between the spring terminals 14 and 15 in the case 12. Furthermore, three grooves 16a to 16c are formed on both the major surfaces of the PTC element 13 so as to extend toward the outer periphery from the center of the major surface of the PTC element 13, as shown in Fig. 1A. The grooves 16a to 16c on one of the major surfaces are formed so as to be opposed to the grooves on the other major surface. The grooves 16a to 16c are provided so as to ensure that the PTC element 13 is divided along the grooves 16a to 16c when it is destroyed at the time of an abnormality. In the present embodiment, the grooves 16a to 16c are formed so as to divide the major surface of the PTC element 13 into three equal divisions. If the grooves formed on the major surface of the PTC element are thus formed so as to divide the PTC element 13 into equal divisions, no extraordinarily large PTC element pieces remain in the case of the destruction, thereby to make it possible to prevent the PTC element pieces from being energized more reliably. The above described grooves 16a to 16c are formed by machining both the major surfaces of the PTC element 13, and the electrodes 13b and 13c are so formed as to also cover inner peripheral surfaces of the grooves 16. If in the PTC element 13, each of the electrodes 13b and 13c is formed by laminating a first electrode layer made of Ni and a second electrode layer made of Ag, either one of the electrodes 13b and 13c may be so formed as to cover the inner peripheral surfaces of the grooves 16. For example, as shown in Fig. 3A, each of the electrodes 13b and 13c may be so formed that only the first electrode layer 19 made of Ni on the lower side leads to the groove 16a formed in the PTC body 13a and the second electrode layer 20 made of Ag does not lead to a portion where the groove 16a is formed. Alternatively, as shown in Fig. 3B, each of the electrodes 13b and 13c may be formed by laminating both the first and second electrode layers 19 and 20 so as to lead to the groove 16a formed in the PTC body 13a. In the PTC device 11 according to the present embodiment, even if the PTC element 13 is destroyed by, for example, the application of an abnormal voltage, the PTC element pieces slip downward between the spring terminals 14 and 15 because the contact portions 17 and 18 of the spring terminals 14 and 15 are not opposed to each other, thereby to make it impossible to elastically interpose the PTC element pieces between the spring terminals 14 and 15. Moreover, the PTC element 13 is destroyed along the above described grooves 16a to 16c, so that no extraordinarily large PTC element pieces are easily formed. Accordingly, the PTC element pieces can be scattered in the case 12, thereby to make it possible to release the electrically connected state with the spring terminals 14 and 15. Fig. 4 is a diagram showing the relationship between electrodes and a PTC element in a PTC device according to another embodiment of the present invention, where Figs. 4A and 4B respectively correspond to Figs. 1A and 1B showing the first embodiment. The second embodiment is constructed similarly to the first embodiment except that the shape of spring terminals and the shape of grooves are altered. Description is made of only the shape of the spring terminals and the grooves formed in the PTC element. In the present embodiment, cross-shaped grooves orthogonal to each other are formed, as shown in Fig. 4A, on both major surfaces of a disk-shaped PTC element 13. Although in Fig. 4A, only grooves 26 on one of the major surfaces are illustrated, grooves in the same shape are also formed in positions opposed to the grooves 26 on the other major surface. Since in the PTC element 13, the direction in which the PTC element 13 is divided is guided by the grooves 26, therefore, the PTC element 13 can be divided into four PTC element pieces in the shape of a fan whose central angle is approximately 90° in the case of the destruction. On the other hand, the PTC element 13 is so constructed that an elastic portion 24a of a spring terminal 24 extend upward and downward, as shown in Fig. 4A, and an elastic portion 25a of the other spring terminal 25 extend in the transverse direction of the drawing. Consequently, the elastic portions 24a and 25a respectively have contact portions 27 and 28 in both their ends. However, each of the contact portions 27 and 28 is brought into contact with the electrode in any one of regions separated by the grooves 26, and only one of the contact portions 27 and 28 is brought into contact with the electrode even in any one of regions separated by the grooves 26. In the PTC device according to the second embodiment, therefore, if the PTC element 13 is destroyed along the grooves 26, the contact portions 27 and 28 of the elastic portions 24a and 25a respectively apply their pressures only to different PTC element pieces. Accordingly, each of the PTC element pieces cannot be interposed between the spring terminals 24 and 25. If the arrangement of the grooves 26 and portions with which the contact portions 27 and 28 of the spring terminals 24 and 25 are brought into contact are so selected that only one of the contact portions 27 and 28 abuts against the electrode in each of the regions separated by the grooves 26 formed on both the major surfaces of the PTC element 13, it is possible to prevent the PTC element pieces from being energized more reliably. Although in the first and second embodiments, the grooves 16a to 16c and 26 are formed on both major surfaces of the PTC element 13 so as to be opposed to each other, the above described grooves may be formed on only one of the major surfaces. Further, even when the grooves are formed on both the major surfaces, the grooves need not be formed so as to be opposed to each other between the major surfaces as described above. Furthermore, the shape of the grooves is not limited to a shape extending outward from the center of the PTC element as shown. Grooves in an arbitrary plane shape can be formed on at least one of the major surfaces of the PTC element so long as the division of the PTC element can be so guided that the PTC element cannot be interposed between the spring terminals. Additionally, although in the above described embodiments, description was made of only the PTC element, the present invention is not limited to the PTC element. For example, the present invention is similarly applicable to an electronic component constructed by containing another electronic component element such as a negative temperature coefficient thermistor element.

Claims: A electronic component comprising: an electronic component element (13) having electrodes (13b,13c) formed on both major surfaces opposed to each other; and a pair of spring terminals (14,15;24,25) electrically connected to the electrodes (13b,13c) of said electronic component element (13) and holding the electronic component element (13) elastically interposed therebetween, portions (14a,15a;24a,25a) which are respectively brought into contact with the electrodes (13b,13c), of said spring terminals (14,15;24,25) not being opposed to each other on both the major surfaces of the electronic component element (13), and grooves (16,26) for guiding the direction in which the electronic component element (13) is divided when it is destroyed being formed on at least one of the major surfaces of said electronic component element (13); characterized in that said portions (14a,15a;24a,25a) of said spring terminals (14,15;24,25) are in a shape having branched portions extending in a radial manner from the center of said electronic component element (13), and said grooves (16,26) extend toward the outer periphery from the center of said at least one of the major surfaces of said electronic component (13), and are arranged such that at least one of said portions (14a,15a;24a,25a) of said spring terminals (14,15;24,25) is in contact with at least one region separated by the grooves (16,26). The electronic component according to claim 1, wherein only one of said pair of spring terminals is brought into contact with the electrode in at least one of a plurality of regions separated by said at least one groove. The electronic component according to claim 2, wherein only one of said pair of spring terminals is brought into contact with the electrode in each of a plurality of regions separated by said at least one groove. The electronic component according to claim 1, wherein said at least one groove is extended in a radial manner toward the outer periphery from the center of the major surface of the electronic component element. The electronic component according to claim 4, wherein said electronic component element has a disk shape. The electronic component according to claim 1, wherein said at least one groove is formed on both the major surfaces of the electronic component element. The electronic component according to claim 6, wherein said at least one groove is formed so as to be opposed to each other on both the major surfaces of the electronic component element. The electronic component according to claim 1, wherein said electronic component element is a positive temperature coefficient thermistor element.

Inventors: ICHIDA SHIGEHIRO, ICHIDA, SHIGEHIRO
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1994
Main classification: H01C1
IPC codes: H01C1, H01C7